#include <cstdio>

using namespace std;

int get_primes(int N) {
  int p = 2, ret = N;
  while (p * p <= N) {
    if (N % p == 0) {
      while (N % p == 0)
        N /= p;
      ret = ret  / p * (p - 1);
    }
    p++;
  }
  if (N > 1)
    ret = ret / N * (N - 1);
  return ret;
}

int main() {
  freopen("fractii.in", "r", stdin);
  freopen("fractii.out", "w", stdout);
  int N;
  scanf("%d", &N);
  long long rez = 1;
  for(int i = 2; i <= N; i++)
    rez += 2 * get_primes(i);
  printf("%lld", rez);
  return 0;
}